The nucleic acid content of some edible mushrooms

Summary An improved method for the determination of nucleic acid content in edible mushrooms is described. Details of tissue homogenization and extraction are also included. In regard to the limit suggested by the Protein Advisory Group of the United Nations System, the amount of nucleic acids found in Agaricus bisporus, Pleurotus cystidiosus, Pleurotus sajor-caju and Volvariella volvacea indicates that it is safe to consume mushrooms as daily vegetable. No significant changes have been found in the nucleic acid content of V. volvacea at different degrees of maturity. V. volvacea loses around 20% of its nucleic acids upon boiling for 10 min. Possible reasons for the discrepancy between the present finding and that given in an earlier report have been discussed.     

A complete separation of dimethylaminoazobenzenesulphonyl-amino acids. Amino acid analysis with low nanogram amounts of polypeptide with dimethylaminoazobenzenesulphonyl chloride.

Triacylglycerol synthesis by glycogen-depleted hepatocytes from fed rats that have low glycerol 3-phosphate contents was stimulated by the addition of glycerol 3-phosphate precursors. Glucagon decreased triacylglycerol synthesis only when it also lowered glycerol 3-phosphate content. The hyperbolic-like relationship between glycerol 3-phosphate content and rates of triacylglycerol synthesis was identical in the absence or presence of glucagon, indicating that the glucagon effect on triacylglycerol synthesis was not mediated through changes in enzyme activities of the esterification pathway but through changes in cellular glycerol 3-phosphate content.     

Lysine metabolism in the human and the monkey: Demonstration of pipecolic acid formation in the brain and other organs

Metabolism ofl-[U-¹⁴C]lysine was studied in the human autopsy tissues and the intact monkeys through intracerebroventricular and intravenous injections. The human tissues were more active in the metabolism ofl-[¹⁴C]lysine to [¹⁴C]pipecolate than the rat tissues previously reported. This metabolism was equally active in the phosphate (pH 7) and the glycyl-glycine (pH 8.6) buffers with the brain and the kidney having higher activity than the liver. Besides [¹⁴C]pipecolate, traces of [¹⁴C]saccharopine and -[¹⁴C]aminoadipate were also detected in the liver incubation. Twenty-four hr after intraventricular injection ofl-[¹⁴C]lysine to the monkey, substantial labeling of pipecolate and -aminoadipate was observed in the brain and spinal cord, with the kidney, liver and the plasma having much reduced levels. Radioactivity levels of these two compounds were found low in the organs and plasma of the intravenously injected monkey. The urine of both monkeys contained only traces of [¹⁴C]pipecolate, even though it contained high levels ofl-[¹⁴C]lysine and -[¹⁴C]aminoadipate. It was concluded thatl-lysine is actively metabolized to pipecolate and -aminoadipate in the human and the monkey, that this reaction is most active in the brain whenl-lysine is intraventricularly administered, and that in contrast to the rat, the monkey may have an effective renal reabsorption for pipecolate which is similar to the human.     

The environment of the sulfhydryl group in human plasma albumin as determined by spin labeling

A series of spin labels, varying in chain length between the maleimide attaching group and the nitroxide free radical, has been used to investigate the environment of the sulfhydryl group in human plasma albumin. From the electron spin resonance spectra, the degree of freedom of the nitroxide was determined and the location of the sulfhydryl was assessed. The effect of bound fatty acids on the sulfhydryl environment was also determined. The environment was found to be analogous to that in the bovine protein, that is, a crevice approximately 9.5 Å deep and not affected in the native state by fatty acids.     

Effect of interferon on phospholipid methylation by peripheral blood mononuclear cells

The effect of human interferon (IFN) preparations on the metabolic pathway leading to the synthesis of phosphatidylcholine (PC) by a stepwise addition of methyl groups to phosphatidylethanolamine (PE) was investigated in human peripheral blood mononuclear (PBMN) cells. An inhibition of the synthesis of PC via this pathway was regularly observed with both alpha- (recombinant or natural) and beta-IFN. This inhibition was apparent within the first 5 min of treatment, reached its maximum between 15 min and 1 hr, and persisted at the same level until 6 hr, the last time point examined. Each of the transmethylated products of PE underwent a similar inhibition, as measured by the turnover rate of individual products. The intracellular pool of the methyl donors, methionine and S-adenosyl-methionine (SAM), was shown to be unaffected. The methyltransferase activity of IFN-pretreated cell extracts was unchanged. These findings support the hypothesis that IFN induces a functional change in phospholipid methylation at the level of organized membrane-bound phospholipid methyltransferase enzymes in intact cells.     

上海生态平衡学术讨论会

中国生态学会“生态平衡”学术讨论会于1981年11月7日至13日在上海召开,来自全国22个省市区的90余名代表出席了会议。大会针对当前国内外广泛重视和关心的“生态平衡”问题展开了热烈地讨论。代表们认为:生态学是社会主义建设蓝图的“底色”,这个“底色”搞不好,社会主义建设也难以搞好,为此,全国人民都要关心生态学的问题。目前污染严重,生态平衡失调,已引起人们的警觉和关注,“生态平衡”问题已提到了议事日程,不允许人们再忽视了。     

The influence of phytoplankton composition on the relative effectiveness of grinding and sonification for chlorophyll extraction

The chlorophyll recovery efficiency was compared between control, ground, and sonified samples. The results showed significant improvement between control and ground samples but not between control and sonified samples. Neither prolonging time of sonification nor using an ice bath during filter grinding improved efficiency. Higher chlorophyll a recovery was obtained from ground samples than from sonified ones, when the water samples contained centric diatoms and filamentous blue-green algae. When total phytoplankton numbers were high, there was a distinct advantage in using grinding rather than sonification for chlorophyll c recovery.Contribution no. 313 of the Great Lakes Research Division, University of Michigan.Contribution no. 313 of the Great Lakes Research Division, University of Michigan.     

Platelet-derived growth factor is a chemoattractant for vascular smooth muscle cells

In previous experiments (Grotendorst et al, 1981), we showed that platelet-derived growth factor promotes the migration of smooth muscle cells in vitro. Using a "checkerboard" analysis, we now establish that platelet-derived growth factor (PDGF) acts as a true chemoattractant for cultured aortic smooth muscle cells. Other growth factors such as epidermal growth factor, fibroblast growth factor, and insulin are not chemoattractants. The chemotactic response occurs before the initiation of DNA synthesis and is not affected by inhibition of DNA synthesis. Chemotaxis occurs at levels of PDGF lower than required for mitogenesis. RNA and protein synthesis are required for the chemotactic response. As found previously in bacteria and leucocytes, we find that methylation reactions are required for the chemotactic response. The possibility is discussed that PDGF acts in vivo at sites of vascular injury to attract smooth muscle cells from the medial layer to the luminal surface, and is involved in the early stages of the formation of atherosclerotic plaques.     

The possible role of soluble salts in chemical evolution

Summary A model is proposed for a prebiotic environment in which concentration, condensation, and chemical evolution of biomolecules could have taken place. The main reactions expected of proteins, nucleic acids, lipids, and some of their precursors in this environment are examined.The model is based on our previously developed concept of a fluctuating system in which hydration and dehydration processes take place in a cyclic manner. In the present model, however, high concentrations of soluble salts, such as chlorides and sulfates, are taken into account, whereas previously a more or less salt-free system had been assumed. Thus the preponderance of surfaces of soluble salts is implied, even though sparingly soluble minerals, such as clay minerals or quartz, are also present.During the dehydration stage biomolecules tend to leave the solution and concentrate at certain microenvironments, such as in micelles and aggregates, at the liquid-gas surface and, possibly, at the emerging solid surfaces. Moreover, in these brines, and especially during the last stages of dehydration, high temperatures are attainable, which may enhance certain reactions between the organic molecules, and result in a net increase of condensation over degradation.In the dehydrated state, solid-state condensation and synthesis reactions are possible in which the surface of soluble salts may serve as a catalyst. Several reports in the literature support this hypothesis. Hydration brings about dissolution of the minerals and redistribution of the biomolecules. In such a system, evolutionary processes like those postulated by White (1980) and by Lahav and White (1980) are possible. Moreover, since several soluble salts of known geological occurrence are optically active in their crystalline state, the involvement of the model system in the selection and evolution of chiral organic compounds should also be considered. In addition, organic molecules in the above microenvironments are also expected to undergo selective interactions based on factors such as molecular pattern and chiral recognition and hydrophobicity. The proposed system emphasizes the need to develop the theoretical background and experimental methods for the study of interactions among biomolecules in the presence of high salt concentrations and solid surfaces of soluble salts, as well as interactions between the biomolecules and these surfaces.